into a larger-diameter chromatin fiber, which then folds into larger loops
juste before cell didvidsion takes place, DNA replicates and the loops
condense even more, forming a pair of chromatids
pair of chromatids = chromosome
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3.6 Protein Synthesis
proteome = all the organisms proteins
gene expression — process in which a geneʼs DNA is used as a template for
synthesis of a specific protein
transcription — the info encoded in a specific region of DNA is transcribed
(copied) to produce a specific molecule of RNA
translation — the RBNA attaches to a ribosome , where the info contained
in RNA is translated into a corresponding sequence of AA to form a new
protein molecule
base triplet — a sequence of 3 nucleotides in DNA also called
codon
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A given codon specifies a particular AA
genetic code — the set of rules that relate the base triplet sequence of
DNA to the corresponding codons of RNA and the AA they specify
Transcription
occurs in the nucleus
3 types of RNA are made from the genetic info represented by the
sequence of base triplets in DNA
Messenger RNA (mRNA) — directs synthesis of a protein
Ribosomal RNA (rRNA) — joins with ribosomal proteins to make
ribosomes
Transfer RNA (tRNA) — binds to an AA and holds it in place on a
ribosome until it is incorporated into a protein during translation
RNA polymerase — catalyzes transcription of DNA
must be instructed where to start transcription process and where to
end it
promoter —a special nucleotide sequence, segment of DNA where
transcription begins
where RNA polymerase attaches to the DNA
During the process base pair in a complementary manner
DNA - RNA
ATGC - UACG
terminator — special nucleotide that specifies the end of the gene
RNA polymerase reaches there and detaches from the transcribed
RNA molecules and DNA strand
introns — regions within a gene that do not code for parts of proteins
exons — regions of DNA that do code for segments of a protein
immediately after transcription, the transcript includes info from both
introns and axons and is called
pre-mRNA
introns are removed from pre-mRNA by small nuclear
ribonucleoproteins (snRNPs) — enzymes that cut out the introns and
splice together the axons
resulting product is a functional mRGNA molecule that posses
through a pore in the nuclear envelope to reach the cytoplasm,
where translation takes place
less genes, making a lot of proteins
dude to alternative splicing of mRNA — a process in which the pre-
mRNA transcribed from a gene is spliced in different ways to produce
several different mRNAs
diff mRNAs then translated into diff proteins
Translation
the nucleotide sequence in an mRNA molecule specifies the AA sequence
of a protein
carried out by ribosomes
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small subunit of a ribosomes has a binding site for mRNA, the larger
subunit has three binding sites for tRNA molecules, a P site, A site and
E site
